The present embodiments relate to amplification of positron emission tomography (PET) signals.
PET may be combined with another imaging modality in a hybrid system. Such multimodality imaging systems may have diagnostic and business value. Both PET/computed tomography (CT) and single photon emission computed tomography (SPECT)/CT multimodality imaging systems allow scans to be performed back-to-back or in a same coordinate system and similar timing. The axial fields of view of the individual modalities are as close together as possible in order to minimize the impact of patient motion and increase correlation of the respective data sets.
Another hybrid example is a brain scan PET system integrated with a magnetic resonance (MR) system. In order for the MR and PET fields of view to overlap, the PET detectors are placed within the MR field of view, as an insert in front of the body coil. The MR body coil is used to excite the hydrogen molecules of the patient by delivering an RF burst. The MR switches into a receive mode, after delivery of the RF burst, and detects RF signals emitted from the patient. The signal-to-noise ratio of the MR received signal is critical to MR image quality. The signal-to-noise ratio is important enough that the MR is typically enclosed in an RF cabin that suppresses RF signals by 100 dB, for both external signals getting into the RF cabin and internal signals getting out of the RF cabin.
Electromagnetic Interference (EMI) and electromagnetic compatibility (EMC) between the MR and PET subsystems is one of the dominant technical challenges facing MR/PET. MR is extremely sensitive to any RF emissions from the PET subsystem, near the hydrogen spin frequency (e.g., roughly 123 MHz+/−500 KHz for a 3 Tesla system). Likewise, the PET front end is extremely vulnerable to the RF emissions from the MR. Coincidence windows of 4-6 nS are typical of non time-of-flight PET scanners, which require that the PET signal chain be stable to 100 pS. For the brain scan PET/MR system, the detector signals are routed out of the RF cabin to avoid EMI and EMC with the MR system. Outside the cabin, the signals are amplified and then passed through an elliptical filter. However, the number and size of cables grows in proportion to the number of PET block detectors.